The fine structure of the receptor neuron and synapses in the stretch receptor organ of the crayfish and the lobster will be studied in various physiological conditions. The effects of divalent cations such as Ca, Mg, and Mn on the inhibitory postsynaptic potential of the crayfish receptor neuron will be studied electrophysiologically. The ultrastructure of the transverse tubules and the triad junctions of the skeletal muscle fiber of the frog will be studied. Major methods used in these studies are electron microscopy and micro-electrophysiology.